Valsartan, also known as (S)—N-(1-Carboxy-2-methyl-prop-1-yl)-N-pentanoyl-N-[2′-(1H-tetrazol-5-yl)bi phenyl-4-ylmethyl]-amine, has the following structure:
and is marketed as the free acid under the name DIOVAN. DIOVAN is prescribed as oral tablets in dosages of 40 mg, 80 mg, 160 mg and 320 mg of valsartan.
Valsartan and/or its intermediates are disclosed in various references, including: U.S. Pat. Nos. 5,399,578, 5,965,592, 5,260,325, 6,271,375, WO 02/006253, WO 01/082858, WO 99/67231, WO 97/30036, Peter Bühlmayer, et. al., Bioorgan. & Med. Chem. Let., 4(1) 29–34 (1994), Th. Moenius, et. al., J. Labelled Cpd. Radiopharm., 43(13) 1245–1252 (2000), and Qingzhong Jia, et. al., Zhongguo Yiyao Gongye Zazhi, 32(9) 385–387 (2001).
Valsartan is an orally active specific angiotensin II antagonist acting on the AT1 receptor subtype. Valsartan is prescribed for the treatment of hypertension. U.S. Pat. No. 6,395,728 is directed to use of valsartan for treatment of diabetes related hypertension. U.S. Pat. Nos. 6,465,502 and 6,485,745 are directed to treatment of lung cancer with valsartan. U.S. Pat. No. 6,294,197 is directed to solid oral dosage forms of valsartan.
The synthesis of valsartan is discussed, inter alia, in U.S. Pat. No. 5,399,578. In the synthesis disclosed therein, the final synthetic step (exclusive of work-up and purification) involves the reaction of a cyano group on the biphenyl ring with an azide, for example, tributyl tin azide. The reaction scheme of the '578 patent is as follows:

Peter Bühlmayer, et. al., Bioorgan. & Med. Chem. Let., 4(1) 29–34 (1994)
In Moenius, et. al., J. Labelled Cpd. Radiopharm., 43(13) 1245–1252 (2000), various schemes for synthesis of valsartan are provided, with one being:

Another paper, Qingzhong Jia, et. al., Zhongguo Yiyao Gongye Zazhi, 32(9) 385–387 (2001), discloses a synthesis scheme for valsartan as follows:

There is a need in the art for an improved synthetic process for the preparation of valsartan and precursors of valsartan.